1. Field of the Invention
The present invention relates to a motor vehicle air-conditioner control apparatus including controllers for discharging a liquid refrigerant stored in a compressor of an air-conditioner mounted on a motor vehicle.
2. Description of the Related Art
As described in Japanese laid-open patent publication No. 8-197938 (hereinafter referred to as xe2x80x9cfirst technical proposalxe2x80x9d), there has heretofore been known a phenomenon in which when a motor vehicle is left daytimes outdoors for a long period of time with its engine shut off, a liquid refrigerant is stored in the compressor of an air-conditioning system on the motor vehicle due to the difference between the temperature in the passenger compartment which rises sharply due to daylight and the temperature in the engine compartment which rises relatively gradually.
A similar phenomenon is also disclosed in Japanese laid-open patent publication No. 6-340213 (hereinafter referred to as xe2x80x9csecond technical proposalxe2x80x9d). The second technical proposal shows that when a motor vehicle is left with its engine shut off, the compressor of an air-conditioning system on the motor vehicle becomes cooler than the condenser in a period of time from morning to evening, and during that time, the refrigerant of the air-conditioning system flows into the compressor and is stored as a liquid refrigerant therein.
Actually, as indicated by experimental results shown in FIGS. 8A and 8B of the accompanying drawings, when a motor vehicle is soaked (left) at night with its engine shut off, the refrigerant is condensed in the condenser of an air-conditioning system on the motor vehicle. Therefore, the amount Lc of a liquid refrigerant (also referred to as xe2x80x9cliquid amountxe2x80x9d) in the compressor is small as indicated by a characteristic curve 2 in FIG. 8A when soaked at night.
From a dawn time tab on, the temperature in the passenger compartment increases due to daylight as indicated by a characteristic curve 4 in FIG. 8B. As a result, the temperature of a piping and an evaporator in a refrigerant circulation system in the air-conditioning system that is disposed in and near the passenger compartment increases gradually.
Therefore, the internal pressure of the evaporator rises, producing a force tending to push up a liquefied refrigerant into the condenser. When the refrigerant exceeds a preset height of the inlet of the condenser, the liquid refrigerant flows back into the compressor that is disposed at the lowermost end of refrigerant circulation system due to an oil return. As indicated by the characteristic curve 2 in FIG. 8A, the amount Lc of the liquid refrigerant increases owing to the daylight-induced temperature rise after the dawn time tab. The characteristic curve 4 in FIG. 8B represents data which are a linear approximation of experimental data.
The amount Lc of the liquid refrigerant sharply increases when soaked daytimes with a large amount of daylight. If the motor vehicle is left daytimes for a long period of time, then the amount Lc of the liquid refrigerant stored in the compressor whose temperature is the lowest in the air-conditioning system, i.e., the refrigerant circulation system, becomes large due to the difference between the thermal capacity of the motor vehicle and the thermal capacity of the air-conditioning system.
It is assumed that when the amount Lc of the liquid refrigerant is full or nearly full at a level xe2x80x9cLARGExe2x80x9d in FIG. 8A, and also when the air-conditioning system is turned off, the engine is started and thereafter the motor vehicle is running at a high speed.
If the air-conditioning system is turned on when the motor vehicle is running at a high speed, then the clutch for transmitting the rotation of the engine to the compressor is engaged to greatly increase the internal pressure of the compressor, thus compressing the liquid refrigerant. When the compressor compresses the liquid refrigerant, it produces a large abnormal noise (liquid compressing noise).
To prevent such a liquid compressing noise from being produced, according to the first technical proposal, when the engine starts to operate at a low rotational speed, the compressor is forcibly operated by the starter motor to discharge the liquid refrigerant stored in the compressor from the compressor at a low rate.
According to the second technical proposal, if the air-conditioning system is activated during a low-refrigerant-temperature activation control waiting time, the compressor of the air-conditioning system is actuated when the rotational speed of the engine is low after the engine is able to sustain continued rotation, thereby discharging the liquid refrigerant to reduce a liquid compression noise. In an air-conditioning system where air from a blower fan is warmed by the engine coolant, the low-refrigerant-temperature activation control waiting time refers to a predetermined time for which the blower fan is turned off when the refrigerant temperature is low and the ambient temperature is low.
According to the first technical proposal, it is necessary for the starter motor to be able to produce a large output, and hence for the starter motor to suffer an increased cost, weight, and volume.
According to the second technical proposal, only when the air-conditioning system is activated during the low-refrigerant-temperature activation control waiting time, the compressor is forcibly actuated. Therefore, under other conditions, the liquid refrigerant is not discharged for reducing a liquid compression noise. The second technical proposal is also problematic in that it is not applicable to a manually operated air-conditioning mode because the second technical proposal is a control process for an automatic air-conditioning mode that is capable of controlling the blower fan.
It is therefore an object of the present invention to provide a motor vehicle air-conditioner control apparatus for discharging a liquid refrigerant stored in the compressor of an air-conditioning system mounted on a motor vehicle for thereby reducing a liquid compression noise.
According to an aspect of the present invention, a clutch is changed from a disengaged state to an engaged state to actuate an air-conditioning system compressor to discharge a liquid refrigerant therefrom when an engine coolant temperature is higher than a predetermined temperature if an air-conditioning system operating switch is detected as being turned on after a startup of an engine is detected.
When the engine coolant temperature is higher than the reference engine coolant temperature, e.g., 40xc2x0 C., the liquid refrigerant stored in the compressor is discharged of its own accord, and hence the amount of the liquid refrigerant stored in the compressor becomes small. Since the compressor is actuated with the small amount of the liquid refrigerant stored therein, the liquid compression noise produced by the compressor is limited to a low level. It is not necessary to actuate the compressor with a starter motor having a large output.
According to another aspect of the present invention, an air-conditioning system compressor is actuated when an engine intake air temperature is higher than a predetermined temperature, e.g., 40xc2x0 C., and lower than a multiple by 1.4, for example, of an engine coolant temperature. The air-conditioning system compressor is thus actuated when the amount of the liquid refrigerant stored therein is smaller than a predetermined amount. Therefore, the liquid compression noise produced by the compressor is limited to a low level. It is not necessary to actuate the compressor with a starter motor having a large output.
According to still another aspect of the present invention, an air-conditioning system compressor is actuated when a passenger compartment temperature is lower than a multiple by 1.2, for example, of an engine coolant temperature if an air-conditioning system operating switch is detected as being turned on after a startup of an engine is detected. The air-conditioning system compressor is thus actuated when the amount of the liquid refrigerant stored therein is smaller than a predetermined amount. Therefore, the liquid compression noise produced by the compressor is limited to a low level. It is not necessary to actuate the compressor with a starter motor having a large output.
According to yet another aspect of the present invention, the amount of a liquid refrigerant stored in an air-conditioning system compressor is judged as being small and the air-conditioning system compressor is actuated to discharge the liquid refrigerant when an engine shutoff time is shorter than a predetermined time, e.g., 4 hours, even when an engine coolant temperature is lower than a reference engine coolant temperature, e.g., 40xc2x0 C., if an air-conditioning system operating switch is detected as being turned on after a startup of an engine is detected. The air-conditioning system compressor is thus actuated when the amount of the liquid refrigerant stored therein is smaller than a predetermined amount. Therefore, the liquid compression noise produced by the compressor is limited to a low level. It is not necessary to actuate the compressor with a starter motor having a large output.
According to yet still another aspect of the present invention, a clutch is changed from a disengaged state to an engaged state to actuate an air-conditioning system compressor to discharge a liquid refrigerant therefrom when an engine intake air temperature is higher than a predetermined temperature, e.g., 40xc2x0 C., and lower than a multiple by 1.4, for example, of an engine coolant temperature, and an engine shutoff time is shorter than a predetermined time, e.g., 4 hours if an air-conditioning system operating switch is detected as being turned on after a startup of an engine is detected. As a result, the air-conditioning system compressor is actuated when the amount of the liquid refrigerant stored therein is smaller than a predetermined amount. Therefore, the liquid compression noise produced by the compressor is limited to a low level. It is not necessary to actuate the compressor with a starter motor having a large output.
According to a further aspect of the present invention, the amount of a liquid refrigerant is judged as being smaller than a predetermined amount and an air-conditioning system compressor can be actuated at a relatively low rotational speed when an engine coolant temperature is lower than a predetermined temperature, e.g., 35xc2x0 C., and an engine rotational speed is lower than a predetermined rotational speed, e.g., 2580 rpm, if an air-conditioning system operating switch is detected as being turned on after a startup of an engine is detected. Therefore, the liquid compression noise produced by the compressor is limited to a low level. It is not necessary to actuate the compressor with a starter motor having a large output.
According to a still further aspect of the present invention, the amount of a liquid refrigerant is judged as being smaller than a predetermined amount and an air-conditioning system compressor can be actuated when an engine intake air temperature is higher than a predetermined temperature and lower than a multiple of an engine coolant temperature and an engine rotational speed is lower than a predetermined rotational speed if an air-conditioning system operating switch is detected as being turned on after a startup of an engine is detected. Therefore, the liquid compression noise produced by the compressor is limited to a low level. It is not necessary to actuate the compressor with a starter motor having a large output.
According to a yet further aspect of the present invention, the amount of a liquid refrigerant is judged as being smaller than a predetermined amount and an air-conditioning system compressor can be actuated at a relatively low rotational speed when a passenger compartment temperature is lower than a multiple of an engine coolant temperature and an engine rotational speed is lower than a predetermined rotational speed if an air-conditioning system operating switch is detected as being turned on after a startup of an engine is detected. Therefore, the liquid compression noise produced by the compressor is limited to a low level. It is not necessary to actuate the compressor with a starter motor having a large output.
According to a yet still further aspect of the present invention, the amount of a liquid refrigerant is judged as being smaller than a predetermined amount and an air-conditioning system compressor can be actuated when an engine coolant temperature is lower than a predetermined temperature and an engine rotational speed is higher than a predetermined rotational speed, on the condition that an engine operating time is longer than a predetermined time, if an air-conditioning system operating switch is detected as being turned on after a startup of an engine is detected. Therefore, the liquid compression noise produced by the compressor is limited to a low level. It is not necessary to actuate the compressor with a starter motor having a large output.